Fuel combustion



Sept. 23, 1941 G. D'ALEN ET AL FUEL COMBUSTION Filed Oct. 2, 1937 3 Sheets-Sheet l a w a INVENTQRS BY LY ATTORNEY.

3 Sheets-Sheet 2 Sept. 23, 1941. G. DALEN ET AL.

FUEL COMBUSTION Filed OO'L. 2, 1957 FIJI! W 7 I If \4 Sept. 23, 1941. G. DALEN ET AL FUEL COMBUSTION Filed 001;. 2, 1937 3 Sheets-Sheet 3 v TQR KM ATTORNEY.

Patented Sept. 23, 1941 FUEL COMBUSTION Gustaf Daln, Lidingo, and Gustaf Erik Bjiirk lund, Stockholm, Sweden, assignors to Svenska Aktiebolaget Gasaccumulator, Stockholm, Sweden, a corporation of Sweden Application October 2, 1937, Serial No. 166,916 r In Sweden February 13, 1932 19 Claims.

This application is a continuation in part with respectto our copending application, Serial No. 655,334 filed February 6, 1933, which matured into Patent No. 2,112,061 on August 20, 1940, and

relatesback thereto, with respect to common more particularly our invention relates to combustion of fuel oil by a method which involves conversion of the liquid fuel into fuel vapor by contact vaporization prior to delivery of the fuel vapor to a combustion zone in which it is brought in contact withthe air required to support combustion.

In one phase our invention relates to heating devices such as cook stoves. water heaters and the like adapted to be operated with natural draft and more specifically to heating devices including heat accumulating mass in the form of relatively large bodies of metal or the like adapted to absorb and accumulate substantial quantities of heat.

-,A principal object of our invention is to provide reliable combustion apparatus of the contact vaporizing type for fuel oil or the like and particularly adapted for continuous burning of fuel over long periods of time and at relatively slow rate. Further objects of the invention and the more detailed nature and manner of carrying it into effect, together with the advantages thereof, may best be understood from the ensuing portion of this specification taken in conjunction with the accompanying drawings forming a part hereof and illustrative of the principles of the invention and of apparatus suitable for carrying it into effect.

In the drawings:

Fig. 1 is a diagram showing the variations of ignition temperatures and dew points of mixture of airand vapor of hydro-carbon fuel with variations in fuel content of the mixtures;

Fig. 2 is a diagrammatic illustration of a primifive embodiment of the invention, further illustrating the principles involved;

Fig. 3 is a vertical cross-sectional view of a r cook stove embodying the invention;

Fig. 4 is a cross-sectional view on enlarged scale showing in detail one form of apparatus usable in the stove shown in Fig. 3;

- Fig. 5 is a vertical sectional view showing an-' other form of combustion apparatus embodying the invention and usable in a stove of the kind shown in- Fig. 3 or other heating apparatus of like kind;

Fig. 6 is a section on enlarged scale showing a part of the structure illustrated in Fig. 5;

Fig. '7 is a view showing a differentform of part of the apparatus illustrated in Fig. 6; and

Fig. 8 is a view showing still another form of such part of the apparatus.

In accordance with the principles of the present invention, liquid fuel is vaporized by contact with a hot vaporizing surface to which the fuel is supplied from a fuel feeding member disposed so that the liquid fuel falls therefrom onto the vaporizing surface. In apparatus of this kind it is necessary that the fuel feeding member be located so that it can be maintained at relatively low temperature in order to prevent premature decomposition of the hydro-carbon fuel in or on the feeding member and the supply conduit leading thereto. Such decomposition would result in the ultimate formation of carbon deposits in the apparatus which would interfere with its proper operation. If the fuel feeding member is located in a zone of low temperature and is maintained at low temperature. it is evident that portions of the confining wall structure between the fuel feeding member and the vaporizing surface must also be at relatively low temperatures. Such relatively cool wall surfaces would form condensation surfaces for fuel vapor if vapor high in fuel concentration were permitted to come into contact therewith and condensation of such vapor would also ultimately lead to carbonization which would interfere with operation 01' the vaporizer.

In accordance with the present invention, the difficulties heretofore encountered in apparatus of the kind under consideration are overcome by the introduction of a dilution gas into the vaporizer in enshrouding relation with the falling liquid fuel which dilution gas may be oxygen bearing and which preferably is air, since air is always a ailable without cost.

If air or other oxygen bearing gas is employed, there arises the possibility of combustion of the oxygen content of the air with the high temperature fuel vapor within the vaporizer structure. Such combustion would be incomplete and of soot-forming nature because of insuilicient oxygen to produce complete combustion of the fuel vapor and consequently must be avoided if the apparatus is to function properly over extended periods of time.

By following the principles of the present inventionit is possible to feed fuel. and vaporize it in the manner indicated above and to supply therewith air or other oxygen bearing dilution gas without incurring the danger either of the ignition of the oxygen content or of the formation of vapor condensate on the burner structure or fuel feeding member. The manner in which this is accomplished will first be explained from the theoretical standpoint in connection with Figs. 1 and 2 of the accompanying drawings.

Referring now to the diagram of Fig. 1, the

ordinates represent the temperature t of the mixture of oil vapor and air in 0., and the abscissae represent the oil content of the mixture, in percentage. The upper curve a in the diagram indicates how the ignition temperature of" the mixture varies with the oil content within the limits of the temperatures supposed to be prevailing in the vaporizer, that is, at temperatures of up to 600. It is evident from this curve that mixtures containing less than about 5% and more than about of oil are not ignitible at the tempreatures prevailing in the vaporizer. Another way of expressing this is by stating that the lower ignition limit of the mixture is at about 5% of oil and the upper ignition limit at about 15% of oil. If the oil content is increased from 5% the ignition temperature will drop first quickly and then gradually more and more slowly to a minimum of about 300 at about 12% of oil. With further increase in oil content the ignition temperature rises again. Ignition and combustion of the mixture will thus take place inside the curve a, within the field marked by crossed lines.

, the mixture, and condensation of oil vapor thus" takes place within the sectioned field lying below I,

this curve.

If air of atmospheric temperature is supplied I to the vaporizer, it is evident that it has to be mixed with oil vapor in such a way that the con-' dition of the mixture, that is, temperature and oil content, varies along a line in the diagram that at no point enters either the ignition field marked with crossed lines or the field lying belowthe dew point curve. As an example, such a line c has been drawn in the diagram, this line representing the formation'of a mixture of increasing'oil content progressing in such a way that air of an initial temperature of 20 may be mixed with hot oilvapor to form a mixture the temperature of which will be higher than the lowest ignition temperature of the oil, for instance 320 0., without either ignition or condensation .occurring.

1 The oil content of the mixture at this tempera ture is about 17% when the formation of the mixture has taken place in accordance with the line 'c. If a line parallel with the base is drawn through the upper end of the line 0, situated at 320, this will intersect the ignition temperature.

curve a at about 7% and 14% of oil, which 011 5 contents are the ignition limits at this temperature. stead taken place along a line d, so that at 320 320 would be attained with a vapor content of less than 7%, for instance with 5%. Then ignition would not occur immediately, but the mixture would gradually absorb more and more of oil vapor, so that the line e would enter the ignition field, as shown by the part e1 of the line, drawn with short dashes. It is evident from the diagram that the field lying between the ignition temperature curve a and the dew point curve b is comparatively wide, and consequentlythe path along which the formation of the mixture can take place without condensation or ignition occurring may vary within wide limits. All that is required is to see to it that before entering a zone of the vaporizer the temperature of whichis higher than the lowest ignition temperature of the fuel (for instance 320) the air should be mixed with oil vapor in such quantity (for instance 17% oil) that owing to the excess of oil the mixture is not ignitible at this temperature, and that the temperature of the mixture formed should all the time be higher than the dew point determined by its composition.

In the apparatus shown in Fig. 2, I is a vaporizer shaped as a high and narrow vessel, which at the bottom is in heat conducting connection with a source of heat, for instance a heated part 2, and at the top is provided with an opening 3 through which air and. fuel may be delivered into the vessel. The fuel enters in liquid state through a nozzle 4 passing through the opening 3, from where it is allowed to fall freely, preferably in the form of drops, upon the bottom of the vessel, which is heated to such a high temperature that the fuel vaporizes immediately as it comes in contact with the bottom. For the carrying away from the vaporizer of the fuel vapor formed and in order that it shall be possible for atmospheric air to enter into the vessel through the opening 3, the vessel is suitably connected to a combustion device, not shown, through a pipe 5 in such a way that'a vacuum is obtained in the interior of the vessel. The ,fuel vapor and the air will thus escape together from the vaporizer through the pipe 5.

It has now been found that if a certain amount of liquid fuel is delivered to the vaporizerper unit of time, and if the area of the opening 3 is given such a size as in view of the vacuum prevailing in the vessel I is suitable, it is possible to obtain such a downward velocity of the air in the vessel [that the fuel vapor is able" to diffuse at the same speed to a certain height peratureto a place at lower temperature. This drop is very nearly linear. The concentration of the fuel vapor may thus be assumed to increase linearly from the said height H to the bottom of the vessel I, at which pure fuel vapor exists. If the concentration of the fuel vapor calculated by percentage is set off in a diagram, as shown in Fig. 2, as the function of the height in the vaporizer, the variation of the concentration is thus represented in the diagram by a straight line It. At that height in the vessel I where the outlet through the pipe is located the mixture of vapor and air formed through the diffusion contains, as shown by the diagram, about 60% of fuel vapor when'the limit layer between the mixture and the pure air is located at the height H. If G kilograms of air are delivered to the vaporizer per unit of time, and if in the vessel between the heights H and H".

The vaporizer is further assumed to be designed in such a way that its temperature decreases from its bottom, where heat is supplied, to its upper part, as shown in Fig. 2. Evidently there is then no risk of ignition of the mixture, as the temperature of the wall of the vessel between the heights H and H" is about 200 and the ignition temperature of the oil mixture is higher than 300, as seen from the diagram in Fig. 1. Neither is there anyrisk of condensation of oil vapor at the heights H and H", as the dew point of the mixture at 5% as well as at 15% of oil vapor is below 150. At the height H for instance the mixture contains 55% of oil vapor, at which composition its dew point is about 180. It is evident from Fig. 2 that the temperature of the wall at this height H' is somewhat above 400, and consequently condensation cannot take place there either. If other points of the wall of the vessel are investigated it will be found that if the concentration of the oil varies according to the line k, the dew point of the mixture is always lying considerably lower than the wall temperature, and consequently no condensation of oil vapor can occur.

If the amount of vapor Q developed per unit of time i maintained at a constant value, and an amount of air larger than G is added per unit of time, for instance G1, the composition of the mixture escaping through the pipe 5 will change accordingly. Let us suppose that G1 is so great that the vapor content of the escaping mixture is reduced to about 40%. At the bottom of the vessel, however, pure oil vapor will still exist,

- and consequently the concentration of this'decreases upwards according tothe line In in the diagram, so that the limit layer between pure air and the mixture willbe located at the height H1. An ignitible mixture, containing for instance 10% of oil vapor, then exists at the height H1', where the temperature of the wall of the vessel is about 350. As the ignition temperature of the mixture at this vapor content is about 300", the mixture will be ignited. On the other hand, condensation of the oil vapor, cannot oohas been increased from G to G1 the limit layer between the pure air and the mixture has become lowered from the height H to the height H1, so that an ignitible mixture has come in contact with points of the wall of the vessel which have a temperature that is sufliciently high for the ignition of the mixture. Such a large amount of air as G1 must thus not be delivered to the vaporizer.

Let us suppose that while maintaining the same vapor quantity Q developed per unit of time, the amount of air supplied is reduced to G2, which is less than the amount of air G, originally supplied. If G2 is so small that the mixture escaping through the pipe 5 contains for instance 75% of oil vapor, then the concentration of the oil vapor in the vessel will vary according to the line k2 in the diagram, and the limit layer between the pure air and the mixture will be situated at the height H2. At the height Hz' the mixture then contains 10% of oil vapor. As the temperature of the wall of the vessel at this height is only slightly below'50" evidently no ignition of the mixture can take place. As the dew point of the mixture at an oil content of 10% is about 90", oil vapor will'however condense on the wall of the vessel at the height of Hz'. For this reason the amount of air used must not be as small as G2.

It is thus evident that the amount of air delivered to the vaporizer per unit of time can be of such a value that neither ignition of the mixture nor condensation on the walls of the vessel is obtained. The quantity 'of air can, however, not be increased above a certain value without an ignitible mixture coming in contact with walls that are so hot that the mixture is ignited. Neither can the air quantity be reduced below a certain value as in that case condensation of oil vapor on the wall of the vessel will take place. The amount of air delivered must therefore be chosen in such a way that at every point at which it comes in contact with the wall of the vessel the mixture formed shall have adew point that is lower than the wall temperature and an ignition temperature that is higher than the wall temperature, provided that its composition falls within the explosion limits. It has been ascertained through experiments that it is suitable to supply per unit of time an air quantity of such a value that the velocity of the air in the vessel will be about of the order of ten centimeters per second.

In order to facilitate the explanation of the principle of the invention it has been supposed in theabove that the concentration of the fuel vapor decreases linearly from the bottom of the vessel to the limit layer that separates the mixture from the pure air. Owing to the escape of the mixture through the pipe 5 and other circumstances the concentration will however not take place perfectly linearly, and the actual composition' of the mixture at difierent points can thus not be determined exactly by means of the diagram. The extent of these deviations are such, however, as to have no appreciable influence on the practical operation of the arrangement. It

cur when the concentration takes place according to the line k1, by reason of the fact that those parts of the wall of the vessel that come in contact with a mixture of given vapor content have an even higher temperature than in the case where the concentration took place according to the line k, in which case condensation could not occur. Owing to the-fact that the air content is always possible to regulate the amount of air delivered into the vaporizer in such a way that the air in the vessel receives a velocity, directed downwards, of such a value that the fuel vapor can diffuse at the same speed upwards through the air current to a certain height that is suitable in view of the temperatures prevailing in the vessel.

If the above indicated theoretical operation is to be obtained it is necessary that at every height in the vessel the mixture should have the same temperature as the part of the wall of the vessel situated at the same height. Asa matter of fact, this is also approximately the case, as the flow in the vessel takes place at very slow velocity, so that there is time for the temperature to become very nearly equalized.

The construction of the vaporizer that is shown in Fig. 2 is not advantageous from a practical point of view. Upon the vaporization of the fuel a violent turbulence occurs'in the lower part of the vessel, which turbulence may extend upwards to the upper parts of the vessel. Fuel concentration of the mixture, continuously decreasing upwards, can then not be obtained through diffusion, but there is a risk that such portions of the mixture that are rich in fuel may come in contact with, the upper cooler parts of the vessel, whereas combustible portions of the mixture may descend into the hotter parts of the vessel and become ignited there.

In order, therefore, to avoid such difficulties it is advantageous in the practical embodiments of the apparatus to provide an auxiliary chamber having relatively small cross-sectional area through which the fuel falls and the entering air flows before reaching themain vaporizing chamber in which turbulence may occur due to the vaporization of the liquid fuel on the vaporizing surface.

Various forms of practical apparatus embodying this invention will now be described, such apparatusbeing shown by way of example as incorporated in cook stove structure.

The stove illustrated in Fig. 3 and indicated generally at In is a cook stove of the accumulating type in which a hot plate l2 for cooking purposes is formed as a part of a relatively heavy mass of metal l4 having a passage I6 therethrough for flow of combustion gases from a burner indicated generally at I8 to a flue pipe 2i) connected to a stack or chimney 22. Advantageously, the part l4 and the burner l8 are surrounded by a large mass of insulating material retained within an outer stove casing 28. During periods of inactivity, the hot plate surface I2 is advantageously covered by a hinged and insulated stove lid 28 to minimize radiation of heat from the surface l2. The burner I8 is adapted to operate continuously so as to continuously maintain the hot plate surface at cook-' ing temperature, the rate of combustion being the fuel vapor space of the burner l8 by a con nection 40 opening into the lower part of chamber 35. Liquid fuel is supplied to the vaporizer through a fuel supply pipe 42 which has a portion 44 extending inside of and spaced from the walls of a conduit 46 which is in communication with the atmosphere at 4 8.

The upper end of the vaporizing chamber 32'.

is closed by a plate 58 which may advantageously be of heat insulating material for reasons to be hereinafter pointed out. Plate 50 is provided with a central opening and this opening is connected with an opening in the pipe 46 by means of a pipe or connection 52 which provides the auxiliary chamber located above and in communication with vaporizing chamber 36.

The portion 44 of the fuel supply pipe, in the embodiment illustrated, is closed at its end as indicated at 54 and the pipe 46 is likewise closed at its inner end by a cap as indicated at 58.

Adjacent to its inner end, the part 44 of the fuel pipe is provided with a downwardly extending tubular part 58 through which depends the fuel feeding member 88 which in this instance is in the form of a pin.

Part 58 extends across the annular-space between parts 44 and 46 and into the upper end of the connection 52 sufficiently to provide an opening 52 of relatively very small cross-sectional area. which opening provides restricted communication for flow of air from pipe 45 to the pipe is upwardly inclined to provide an air trap the part H by conduction away from the cooking 3 surface l2.

Air for combustion of the fuel in burner 18 is supplied through the air inlet pipe 30. The construction of the burner may vary widely within the scope of the invention, any suitable known burner structure for combustion of fuel vapor with air being usable. One such form of burner structure will be described hereinafter in conjunction with Flgs. 5 and 6.

The fuel vaporizer indicated generally at 32 i is in the embodiment illustrated formed integral with and as a part of a heavy metal member 34.

having a contact vaporizing surface 38 at the bot- 1 tom thereof and this chamber is connected to at the inner end of the fuel line for maintaining a constant level of fuel, as indicated at 58 which is Just above the level of the top of the part 58, so that fuel may flow by gravity through the fuel pipe and drop from thev lower end of the feeding member, either in the form of a series of drops or in the form of a small stream, depending upon the rate at which fuel is supplied. Ordinarily, for apparatus of this kind in which combustion is relatively slow, the supply of fuel will be in the form of a series of drops.

Referring now more particularly to Figs. 5 am 6, the apparatus illustrated in these figures comprises a stove indicated generally at In and having a gaseous fuel burner l8, the lower portion of which is shown in Fig. 5 and which comprises perforated vertically extending burner tubes II and 12, the lower ends of which are seated at ditferent levels in the lower burner member 34 which is provided with the integral vaporizer 32 haw ing the vaporizing chamber 36 and contact vaporizing surface 38. The lower part of chamber 38 is connected by means of the passage 40 to the vapor space 14 formed in the burner member 34. Air is admitted to the interior of burner pipe 12 through the pipe 30 and combustion takes place at the perforations along the burner'pipe due to flow of air into the vapor space.

In this embodiment, the lower burner member is surrounded by insulation-18 retained in a casing 18 located in a space 88 formed by casing parts 82 extending into the main mass of insulation 24 through which the upper portion of the burner extends. I

Atmospheric air is admitted to the space 88 through a suitable opening 84 and from this space flows to the air inlet pipe 30. Air also flows from space 80 into the space 86 around the outer burner tube I and through the perforations in this tube to the combustion space I4 between tubes I0 and I2.

As in the embodiment previously described, the upper end of the vaporizer chamber 36 is closed by a cover plate 50 which is advantageously covered with insulating material as at 88, through which the connection 52, forming the auxiliary chamber, passes.

In the upper part of the space 80, and supported by a part of the casing structure 82, there is located a fuel supplying member 90 having a bore 92 therethrough and terminating at its outer end in a fuel receiving receptacle 94 to which fuel in regulated amount is fed from a supply pipe indicated at 96.

The part 90 is shouldered to support one end of a tube 98 which at its opposite end is screwed into a socket formed in a hollow part I00. The lower end of the part I00 rests on a cap I02 having a central opening I04 centered over the upper end of the connection 52. The inner end of bore 92 is counter-bored to receive one end of a fuel supply pipe I06, the inner end of which is bent downwardly and shaped to provide a fuel feeding nozzle I08 centrally located above the connection 52 and the opening I04.

Part 90 is also provided with a sleeve like extension I I0 at its inner end which supports a baflle tube 2 concentric with and spaced from both the inner fuel supply pipe I06 and the outer pipe 98. At its inner end, the tube H2 is open, this tube being advantageously somewhat shorter than the pipes between which it is located.

Part I00 is provided with a small air admission orifice II4 which is in communication with the space 80 and the assembly of parts comprising the part 02 and the part attached thereto is advantageously covered by a sheet metal shroud or baflle IIG.

Having in mind the principles discussed in connection with Figs. 1 and 2, we will now proceed to a consideration of their operation in the apparatus shown in Figs. 4 to 6.

Oil fed to the apparatus falls freely under the influence of gravity alone from the tip of the fuel feeding member, that is, pin 60 or nozzle I08 as the case may be, onto the vaporizing v surface 38 of the vaporizer. It will be understood that surface 38 is maintained at extremely high temperature since it is in direct heat transmitting relation with the lower portion of the combustion zone of the burner. As will be seen from Fig. 5, if the burner is of the specific kind therein illustrated, the flames produced at the lower part of the burner tube 12 direct their heat substantially directly against the walls of the lower burner member in which the vaporizing chamber is formed. It will be understood however that the vaporizing chamber and vaporizing surface may be maintained at high temperature by other means.

Due to the high temperature of the vaporizing surface, which is conveniently termed a contact vaporizing surface, the oil is very rapidly vaporized as soon as it hits this surface.

As the liquid fuel is vaporized by contact with the vaporizing surface, the vapors formed therefrom fill the vaporizing chamber and although these vapors are relatively heavy, their highly heated state and the quantity of vapor produced are such that the vapors will tend to rise through the vaporizing chamber and diffuse upwardly through the auxiliary chamber against the flow of the restricted quantity of air admitted to the latter and flowing downwardly therein from the air admission orifice (62 in Fig. 4 and H4 in Fig. 6). The downward flow of air is, of course, created by the negative pressure caused in both the vaporizing chamber and the auxiliary chamber by the draft created by the burner. In accordance with the embodiments of the invention in which an auxiliary chamber is employed, the air admitted is so restricted by the orifice that the rate of flow downwardly through the auxiliary chamber is sufficiently slow to permit the rising fuel vapor to commence to mix with the air in the auxiliary chamber and to mix therewith in suflicient quantity to produce an incombustibly rich mixture before the air can be drawn into the vaporizing chamber proper. The zone of combustible air-fuel mixture may, for example, be within the space I20 limited by the dotted lines indicated in rigs. 4 and 6, which lines correspond to the lines H and 1-1" in Fig. 2. The more remote location of the walls of the auxiliarychamber from the source of heat, together with the influx of fresh air which is comparatively cool, maintains the temperature within the auxiliary chamber at a value which is below ignition temperature for the combustible mixture. Consequently, combustion will not take place at the level of the space I20 and by the 7 time the oxygen content of the air has been drawn downwardly into a hotter zone where ignition temperatures exist, the concentration of fuel has increased to such a degree that the mixture is incombustible. Thus, if the air is admitted in sufficiently restricted quantities and with sufiiciently low velocity, having regard to the capacity of the burner and the vaporizer, oxygen bearing air or other dilution gas can be introduced into the vapor filled vaporizing chamber,

which is at ignition temperature, without cansing soot producing combustion.

While as pointed out above, the walls of the vaporizing chamber formed by the connection 52 are at lower temperature than that necessary to produce ignition of fuel, it will be apparent that because of their connection with the main vaporizing structure, these walls will be maintained at elevated temperatures which may readily be maintained above the dew point of the mixture being progressively enriched with fuel as the air flows downwardly through the auxiliary chamber. It will further be appreciated that the extreme upper end of the auxiliary chamber may very readily be below the dew point of a mixture having an appreciable vapor content. Consequently, the size of the air admission orifice must be so related to the size and capacity of the particular burner and the draft conditions applying thereto, that sufficient air will be admitted to prevent diffusion of vapor upwardly in the auxiliary chamber to an extent such that a mixture is formed therein having a dew point higher than the temperature of the walls with which it comes in contact.

The proper size or area for the air admission orifice may readily be calculated according to .known laws, but by way of example-it may be stated that we have found the maximum permissible diameter of the air admitting orifice to be of the order of three millimeters in the case of vaporizing equipment for a domestic cook stove or the like operating with natural draft and having a vaporizing chamber the height of which .at the desired temperature.

is in the neighborhood of seventy-five millimeters and provided with an auxiliary chamber the inside diameter of which is approximately twelve millimeters. In the case of an annular opening as shown in Fig. 4, the maximum area thereof would correspond approximately to that of a circular opening of three millimeters diameter.

Generally speaking, the deisred results may be obtained, from the standpoint of preventing undesired turbulence and also from the standpoint of providing a proper zone in .which the mixture may pass through the combustible stage without ignition and may also be formed without difllculty due to condensation, if the passage provided in the auxiliary chamber between the fuel feeding member and the main chamber is at least twice as long as its diameter.

In addition to the prevention of condensation of fuel vapors on the relatively cool surfaces at and adjacent to the fuel feeding member, the introduction of oxygen bearing dilution gas has other important functions. Complete vaporization of the heavy fractions of the oil may not occur in practice in apparatus of this kind and as a result small quantities of carbonaceous residue, usually in the form of coke deposits, are

- formed at the point of contact of the oil with the contact vaporizing surface, as indicated at H8 in Figs. 4 and 5. Further quantities of oil will consequently fall on this residual deposit rather than directly onto the metallic surface and the surfade of such deposit may accordingly be considered as a part of the contact vaporizing surfaces Under normal operating conditions, this deposit will be at oil vaporizing temperature.

By introducing an oxygen bearing dilution gas such as air, oxygen is carried into the vaporizing chamber and owing to the turbulence therein,

vaporizer through walls 52, member I00, and the walls of the tube 08. As shown in this figure and also in Fig. 6, the walls 52 are preferably of thin section so as to provide a poor path for heat conduction to the member I00. On the other hand, the walls 98 are advantageously made of substantially heavier section to provide for rapid heat conduction between member I00 and the relatively cool member 80 or 000 as the case may be. By this arrangement the flow of heat by conduction is controlled in such manner that the portion of the apparatus associated with the liquid fuel supply may be maintained relatively very cool so that no danger exists of decomposition of the fuel before it is delivered from the fuel feeding member.

Further, as shown in Fig. 7, the air admission I restriction of the air flow to suit individual insome of this oxygen is carried into contact with so that the burner may be operated continuously.

over long periods without building up a solid deposit of residue of suflicient magnitude to inter- .fere with proper vaporization of the oil fallin thereon. For this reason, as well as for the purpose of preventing condensation in the zone where the air mixes with fuel vapor, it is advantageous to supply as much air as may safely be admitted without running the risk of having the zone where a combustible mixture is formed occur at a place in the structure which is above ignition temperature.

In the arrangement illustrated in Fig. '7, means are shown which may in some instances advantageously be employed to assist in maintaining the upper portion of the wall structure of the auxiliary chamber and the fuel feeding member This means may be used with or without heat insulating material for the cover of the vaporizing chamber as shown at disclosed, the member 90a is formed with heat' dissipating fins 00b whereby to dissipate rapidly any heat conducted to this memberfrom the stallations which may vary somewhat as to the amount of draft and consequently the amount of pressure drop across the orifice. .It will be understood that such adjustment may be made by having orifice plugs having different size bores.

Referring particularly to the forms of apparatus shown in Figs. 5, 6, and '7, it will be noted that the open ended tube 2, in association with the inner and outer tubes I06 and 98, provides a labyrinth creating a relatively very long path of travel for oil which may tend to creep because of surface tension along the exterior surface of the tube I06 from the feeding nozzle I08, before such oil can reach a surface sufliciently hot to cause carbonization of the oil and consequent clogging of passages.

From the nature of the data hereinabove given with respect to dimensions and air velocity suitable for apparatus of the kind described, it is evident that the quantity of air admitted is relatively small and the restricting orifice through which it is admitted is also quite small and in some cases liable to partial clogging from small accumulations of dust or the like. If partial clogging of the orifice occurs, the reduction in the quantity and velocity of flow of air into the auxiliary chamber may be such as to permit the fuel vapor to diffuse to an undesired height in the auxiliary chamber and form a mixture in the upper or cooler portion of the chamber, the dew point of which mixture is above the temperature of the walls of such cooler part. This would, of

course, cause some condensation of vapor on these walls. In order to guard against such contingency, the auxiliary chamber may advantageously be formed as illustrated in Fig. 8, by shaping the walls of the connection 520. so that the auxiliary chamber is of increasing cross-sectional area in the direction toward the vaporizing chamber, particularly with respect to the lower portion thereof. In order to achieve the desired form of auxiliary chamber, the connection 52a may most conveniently be made frusto-conical as shown in the figure. With a construction of this character, {the velocity of the air flowing toward the rising fuel vapor decreases. Conversely, it may be said that the fuel vapor as it rises, progressively meets air of constantly increasing velocity in opposed direction. Consequently, if the air admission orifice becomes partially clogged and as a result the fuel vapor tends to diffuse to a higher level in the auxiliary chamber, this tendency is counteracted by the increased velocity of the air which it meets, and the net result is to mitigate, if not entirely counteract, the effect of a partially clogged air admission orifice.

Furthermore, from a practical standpoint, the

. conical form of auxiliary chamber reduces the possibility of liquid fuel striking the wall of the auxiliary chamber as it falls from the fuel feeding member, even if for any reason the apparatus is tilted somewhat from its correct position.

While the invention has been described in conjunction with apparatus operating with natural draft, it will be evident that it is not limited to natural draft devices.

Also, the principles of the invention may be embodied in apparatus in which a mixture of fuel vapor and dilution gas of homogeneous nature is provided through which the liquid fuel falls, rather than through a mixture of progressively increasing vapor content as in the embodiments described. It a homogeneous mixture is provided, it will be evident from the diagram in Fig. 1, that such mixture, if. it contains fuel, will not condense if surfaces with which it comes in contact are maintained at a temperature higherthan about 120. Also, in a case such as this, risk of ignition of the mixture is not present since the upper limit of ignition or combustion is reached with a fuel content of approximately The invention is accordingly not to be considered as limited to the embodiments shown but is to be considered asembracing all that falls within the scope of the appended claims when they are construed as broadly as is consistent with the state of the prior art.

What we claim is:

l. The method of producing heat by the aid of a vaporizer having a vaporizing chamber and a hot contact vaporizing surface which includes causing liquid hydro-carbon fuel to fall onto said surface and forming vapor thereof, flowing an oxygen-bearing gaseous fluid of different chemical nature than the hydro-carbon fuel into contact with the falling fuel at a temperature below the ignition temperature of said vapor, enshrouding the falling fuel with said gaseous fluid, restricting the quantity of said flowing gaseous fluid to a degree causing the gaseous fluid to be mixed with said vapor to form a mixture so rich in fuel vapor as to be non-combustion supporting before a zone of ignition temperature is reached by the flowing gaseous fluid, withdrawing the non-combustion supporting gaseous contents of said vaporizing chamber, mixing such contents with sufficient air after withdrawal from the chamber to provide a combustion supporting mixture, and burning said combustion supporting mixture.

2. The method ofproducing heat by the aid of a vaporizer having a vaporizing chamber and a hot contact vaporizing surface which consists in causing liquid hydro-carbon fuel to fall through said vaporizing chamber onto said vaporizing surface; enshrouding the falling fuel in an envelope of air having a relatively low temperature flowipg into-said chamber, preventing combustion of fuel vapor formed in said chamber with said air by restricting the quantity of air to a degree causing the formation of a mixture of said air and said fuel vapor so rich in fuel as to be non-combustion supporting before said flowing air reaches a zone of ignition temperature, withdrawing the non-combustion supporting gaseous contents of said chamber, mixing the non-combustion supporting gas after withdrawal from the chamber with air to form a combustion supporting mixture, burning said combustion-supporting mixture and utilizing heat produced thereby to maintain said contact vaporizing surface at fuel vaporizing temperature.

3. The method of producing heat by the aid of a vaporizer having a vaporizing chamber and a hot contact vaporizing surface which comprises causing liquid hydro-carbon fuel to fall onto said surface, enshrouding the falling fuel in an envelope of oxygen-bearing gaseous fluid having a relatively low temperature flowing into said chamber, restricting the quantity of gaseous fluid admitted to a degree causing it to form a combustion supporting mixture with the fuel vapor before reaching a zone of ignition temperature and to form a mixture sufficiently rich in fuel so as to be non-combustion supporting by the time it reaches a zone of ignition temperature, utilizing the oxygen content of said gaseous fluid to oxidize solid carbonaceous deposits formed on said vaporizing surface, withdrawing the gaseous contents from said vaporizing chamber in noncombustion supporting state, mixing the gases after withdrawal from the vaporizing chamberwith air to form a combustion supporting mixture, and burning said combustion supporting mixture to produce heat.

4. That improvement in the art of producing heat by the aid of a liquid fuel vaporizer having a main vaporizing chamber with a hot contact vaporizing surface in said main chamber and an auxiliary chamber above said main chamber, which consists in the method of causing the liquid hydro-carbon fuel to fall through said auxiliary chamber and said main chamber onto said vaporizing surface and forming vapor thereof, admitting air having a temperature below the ignition point of the fuel to said main chamber through said auxiliary chamber in an envelope enshrouding the falling fuel, whereby to prevent fuel vapor diifused from the falling fuel toreach and condense on the wall surfaces of said auxiliary chamber, restricting the quantity of air admitted so as to cause the air to mix with fuel vapor rising from said main chamber in a zone in said auxiliary chamber having a temperature below the ignition point and to cause a mixture so rich in fuel as to be non-combustion supporting to be formed before the air reaches the main vaporizing chamber, utilizing the oxygen content of the air to oxidize solid carbonaceous residue formed on said vaporizing surface, withdrawing the gaseous contents of the main vaporizing chamber in non-combustion supporting form, mixing such contents with air to form a combustion supporting mixture and burning the combustion supporting mixture to produce heat.

5. Liquid fuel combustion apparatus comprising structure providing a fuel vaporizer having a main vaporizing chamber, a contact vaporizing surface and an auxiliary chamber above said main chamber, a liquid fuel feeding member arranged to have fuel fall therefrom through said chambers onto said vaporizing surface and means for admitting a gaseous fluid of different chemical nature than said hydro-carbon fuel at a. temperature below the ignition point of said fuel to said main vaporizing chamber in an envelope'enshrouding the falling liquid fuel, the quantity of such gaseous fluid being restricted to a degree causing a mixture of said gaseous fluid and fuel vapor too rich in fuel to be combustion supporting to be formed in said auxiliary chamber before such gaseous fluid reaches said main vaporizing chamber.

6. In liquid fuel combustion apparatus, a burner, a vaporizer for supplying fuel vapor to said burner, said vaporizer including a main vaporizing chamber, a contact vaporizing surface insaid chamber and an auxiliary chamber above said main chamber providing a passage of increasing temperature in the direction approaching said main chamber, a liquid fuel feeding memgen-bearing gaseous fluid of different chemical nature than the hydrocarbon fuel and having insufficient oxygen to form acombustion supportber for causing liquid hydro-carbon fuel to fall through said passage onto said vaporizing surface, an oriflce for admitting air at a temperature below the ignition point of said fuel to the upper part of said passage, said orifice being dimensioned'to restrict the quantity of air admitted so that it is mixed with-suflicient vapor rising from said main vaporizing chamber to form a mixture so rich in fuelas to be non-combustion supporting by the time a temperature zone is reached which is at ignitiontemperature.

7. Liquid fuel combustion apparatus comprising a vaporizer having wall structure forming a main chamber and an auxiliary chamber of substantially smaller cross-sectional area than the.

cross-sectional area of said main, chamber, said auxiliary chamber being above and in communication with said main chamber, a liquid feeding member in said auxiliary chamber disposed to have liquid drop or pour therefrom into said main chamber, means to supply liquid hydrocarbon fuel to said feeding member, and means to supply to said auxiliary chamber oxygen-bearing aseous fluid of different chemical nature than the hydrocarbon fuel at a temperature lower than the vaporization temperature of the light hydrocarbon in the liquid fuel and having insufllcient-oxygen to form a combustion supporting mixture with the vaporized fuel in said main chamber.

8. Liquid fuel combustion apparatus comprising wall structure forming a combustion zone, a vaporizer disposed in'heat-receiving relationship to said wall structure and having a main chamber and an auxiliary chamber above and in comto form a combustion supporting mixture in said main chamber with vapor of the hydrocarbon fuel, said auxiliary chamber being relatively narrow horizontally to provide sumcient flow of the gaseous fluid to prevent condensation on the'wal thereof of vapor of the hydrocarbon fuel.

9. Liquid .fuel combustion apparatus comprising wall structure forming a combustion zone, a vaporizer disposed in heat-receiving relationship to saidwall structure and having a vaporizing chamber, a liquid feeding member disposed to have liquid drop or pour therefrom into said chamber, means to supply liquid hydrocarbon fuel to said feeding member, said vaporizing chamber having a hot surface vertically below said feeding member, means to introduce into said vaporizer at a temperature very much lower than the temperature of said hot surface an oxying mixture in said vaporizing chamber with the vapor of the hydrocarbon fuel, means for withdrawing from the vaporizer the non-combustion supporting gas mixture of fuel vapor and gaseous fluid formed in the vaporizer. and means for supplyingcombustion air to said gas mixture subse-' quent to its withdrawal from the vaporizer to provide a combustion supporting mixture for combustion in said combustion zone.

10. Liquid fuel combustion apparatus .comprising wall structure forming a combustion zone, a vaporizer disposed in heat-receiving relationship to said wall structure and having a main chamber and an auxiliary chamber above said main chamber and in communication therewith, a liquid feeding member in said auxiliary chamber disposed to have liquid drop or pour therefrom into said main chamber, means bustion supporting mixture in said main chamher with vapor of thehydrocarbcn fuel, means .for withdrawing from said main chamber the non-combustion supporting mixture formed in said main 'chamber and means for supplying combustion air to said gas mixture subsequent to its withdrawal from the main chamber to provide a combustion supporting mixture for combustion in said combustion zone.

11. In liquid fuel combustion apparatus, means providing a vaporizing chamber, a liquid fuel feeding member having a tip located above the vaporizing chamber and adapted to have fuel fall therefrom into the chamber, and wall structure in contactwith said member but spaced from said tip and providing an enclosing passage communicating with said chamber and in which said tip is located and through which the fuel falls, said wall structure forming a labyrinth providing an extended path of travel for preventing a film of oil from creeping on the surface of said wall structure from the tip of said feeding member to the wall of the vaporizer.

12. In liquid fuel burning apparatus, means providing a vaporizing chamberadapted to be continuously maintained at high temperature, a liquid fuel feeding member having a feeding tip disposed above said chamber and arranged to have liquid fuel fall therefrom into the chamber, wall structure spaced from said tip providing a passage between said tip and said chamber through which the fuel falls, said feeding member comprising a conduit extending laterally from said feeding tip, the wall structureat the upper end of said passage extending laterally to provide a space between said conduit and the laterally extending walls, the end of said space remote from the feeding .tip being closed, means in said space providing an extended surface labyrinth, and an orifice for, admitting a restricted amount of air to said passage in the vicinity of said feeding tip, the major portion of the space between the laterally extending fuel feeding conduit and the spaced enclosing walls constituting a dead air space.

13. In liquid fuel burning apparatus, structure providing a vaporizing chamber adapted to be maintained at high temperature, means providing an auxiliary chamber extending upwardly from the vaporizing chamber, a liquid fuel feeding conduit having a feeding tip located in the upper part of said auxiliary chamber, an orifice for admitting air to the upper part of said auxiliary chamber for flow therethrough to said vaporizing chamber, wall structure providing a closed passage extending laterally from said auxiliary chamberand in communication with the upper portion thereof, said fuel feeding conduit extending through and in contact with said wall structure into said passage and being spaced from the walls of the passage, and means providing an extended surface labyrinth around said conduit.-

14. The method of vaporizing liquid hydrocarbon fuel by the aid of a vaporizer having a hot contact vaporizing surface which includes causing the liquid fuel to fall onto said surface from a place having a temperature below the vaporizing temperature of the fuel and forming vapor thereof, flowing an oxygen bearing gaseous fluid of different chemical nature than that of the fuel at a temperature below the ignition temperature of the fuel, enshrouding the falling fuel with said gaseous fluid, and regulating the quantity of gaseous fluid admitted so asto cause the gaseous fluid to form a mixture with said vapor rich enough in fuel vapor so as to be noncombustion supporting before a zone of ignition temperature is reached by the flowing gaseous fluid but lean enough in fuel vapor to maintain the dew point of the mixture below the temperature of the walls of the vaporizer structure with which it comes in contact.

15. That improvement in the art of vaporizing liquid hydro-carbon fuel by the aid of a vaporizer having a vaporizing chamber with a hot contact vaporizing surface therein, which includes the method of causing the liquid fuel to fall to said vaporizing surface from a feedin member outside said chamber through a passage having a smaller cross-sectional area than that of said chamber, admitting relatively cool air to said passage, to flow into said chamber in enshrouding relation to the falling fuel and in the same direction, and restricting the quantity of air admitted to an extent such that vapor formed in said chamber diffuses into the air in said passage to form in said passage a mixture so rich in fuel as to be non-combustion supporting before a zone of ignition temperature is reached.

'16. A vaporizer for liquid fuel including a vaporizing chamber having an outlet for vaporized fuel and a hot vaporizing surface, an auxiliary chamber located above said vaporizing chamber and in communication therewith, a fuel feeding member located in said auxiliary chamber and arranged to have liquid fuel fall therefrom through said chambers to said vaporizing surface, an orifice for admitting a restricted quantity of air at a temperature below the ignition point of said fuel to said auxiliary chamber to flow therethrough to the vaporizing.

chamber in enshrouding relation with the falling fuel, said auxiliary chamber having a length between the fuel feeding member and the vaporizingchamber at least twice as long as its diameter and said orifice restricting the admission of air to said auxiliary chamber to an extent permitting vapor from the vaporizing chamber to diffuse upwardly into said auxiliary chamber against the flow of air therein to an extent forming a mixture of fuel vaporand air so rich in fuel as to be-non-combustion supporting before a zone of ignition temperature is reached.

1'7. A vaporizer for liquid fuel including a vaporizing chamber having an outlet for fuel vapor and a hot vaporizing surface, an auxiliary chamber located in a relatively cool zone above said vaporizing chamber, a fuel feeding member located in said auxiliary chamber and spaced from said vaporizing chamber, said fuel feeding member being arranged tohave liquid fuel fall therefrom through said chamber to said vaporizing surface, and an orifice for admitting a restricted quantity of air to flow in enshrouding relation with the falling fuel through the auxiliary chamber toward the vaporizing chamber, the portion of said auxiliary chamber adjacent to the vaporizing chamber being of increasing cross-sectional area in the direction of flow of air therethrough.

-18. A vaporizer for liquid fuel including a vaporizing chamber having an outlet for fuel vapor and a hot vaporizing surface, an auxiliary chamber located in a relatively cool zone above said vaporizing chamber, a fuel feeding member located in said auxiliary chamber and spaced from said vaporizing chamber, said fuel feeding member being arranged to have liquid fuel fall therefrom through 'said chamber to said vaporizing surface, and an orifice for admitting a restricted quantity of air to flow in enshrouding relation with the falling fuel through the auxiliary chamber toward the vaporizing chamber, the portion of said auxiliary chamber adjacent to the vaporizing chamber being of generally conical.form and of increasing cross-sectional area in the direction of flow of said air.

. 19. A vaporizer for liquid fuel including means providing a vaporizing chamber, an auxiliary chamber in communication with said vaporizing chamber, a fuel feeding member located in said auxiliary chamber and arranged to have liquid fuel fall therefrom into said vaporizing chamber, an orifice for admitting a restricted quantity of-air to flow through said auxiliary chamber in enshrouding relation with the falling fuel, wall structure extending from said auxiliary chamber and providing a closed passage in communication with said auxiliary chamber, a fuel feeding conduit extending through said passage, and heat dissipating means in heat conducting relation with said wall structure and said fuel feeding conduit for retarding conduction of heat through said wall structure to said conduit. GUSTAF DALEN. 

